This project represents a continuation of Dr. Cohen's well known studies on the psychobiological factors which influence individuals' susceptibility to the clinical manifestations of viral infections. In this particular series of studies, particular emphasis will be placed on the effects of marital relationships. The study will be a prospective analysis of 160 healthy volunteers, of whom 2/3 will be married, who receive an initial evaluation on hypothesized predictors and mediators of illness, and who will be subsequently inoculated with one of tow viruses that cause a mild influenza illness. The investigators will monitor indicators of infection and illness expression over the next 7 days after inoculation. Despite the fact that 98% will become infected, only about 40% will develop signs of "illness," and the latter will be the main outcome variable. The specific aims are to: (1) identify the characteristics of marital and non-marital relationships that contribute to resistance; (2) determine the influence of personality characteristics; (3) determine the biological pathways by which social relationships influence resistance; and (4) assess the influence of demographic variables such as age, SES, and perceived social status on resistance to infection. The rationale underlying the study is that there is a lot of suggestive but not conclusive evidence that married people are generally healthier than single or formerly married people, but the causal relationships and biological pathways mediating this association is unknown. During the 2 months before the study subjects will undergo extensive evaluation that will include personality and socials environment questionnaires, urine collection for catecholamines, and repeated salivary cortisol samples. For the study itself they will be housed in a hotel, where they will remain for 8 days. At the end of the first day they are inoculated with the virus, and during the ensuing week they are closely monitored for symptoms, measurement of the virus and antibodies, salivary cortisols, and daily affect and health practices. The major independent variable in the analysis will be the quality of the marriage: unmarried, low quality, or high quality. It is hypothesized that a high quality marriage will result in less illness expression.